Syria’s military sent tanks to neighborhoods on the outskirts of Damascus Sunday in an attempt to quell the most intense fighting yet seen so close to the capital, one day after the Arab League announced it would suspend its observation mission.

The spike in violence throughout the country – rights groups say more than 100 people have been killed since Thursday – comes days before the UN Security Council plans to vote on a resolution calling for President Bashar Al Assad to step down. The UN says more than 5,400 people have died so far in Assad’s crackdown on an uprising against his regime.

The Associated Press reports that nine people died over the last day in clashes on the eastern edges of Damascus. Rights activists said that three people died in fighting in the suburb of Kfar Batna, and reported heavy shelling in that area as well as nearby suburbs. The state news agency, meanwhile, reported that an “armed terrorist group” bombed a bus carrying army personnel, killing six people and injuring six others. The state news agency said the bomb was a remotely detonated.

The government attack on the suburbs began after the Free Syrian Army, largely made up of defectors from Syria’s military, occupied the area, reports the BBC. According to activists, the assault involved more than 2,000 troops and 50 tanks. Rami Abdul Rahman, head of the UK-based Syrian Observatory for Human Rights, told the BBC that “the Syrian regime is trying to finish the uprising militarily now that the case is being taken to the United Nations."

Head of the Arab League Nabil Al Arabi announced yesterday that the League’s observers would immediately suspend their nearly five-week monitoring mission because of “a severe deterioration of the situation and the continued use of violence.” The mission was intended to observe whether Syria was complying with an Arab League plan adopted in November to end the violence. The New York Times reports that Mr. Arabi blamed the Syrian government for the violence, saying it had decided to escalate the crackdown. The Times reports that the observers ventured on Saturday to the outskirts of Rankous, which was nearly empty after five days of government shelling and fighting. But they turned back after a warning from army officers that rebels might use explosives.

The monitoring mission has faced criticism of its effectiveness for weeks. Now that it has ended, pressure is increasing for the Security Council to take action. The Syrian National Council, the main opposition group, sent a delegation to the UN to “demand international protection for civilians,” reports the Financial Times. Adding to the urgency, the conflict in Syria is becoming increasingly militarized, with army defectors and some opposition activists using arms to fight the government in what increasingly looks like a civil war. A member of the Syrian National Council expressed concern Thursday about the armed groups, saying they must work together with the political opposition, reports the Monitor.

The Security Council is due to vote on Jan. 31 on a resolution that would affirm an Arab League transition plan. Russia, an ally of Syria, opposes the resolution. Bloomberg reports that a draft resolution discussed on Jan. 27 changed language that had previously called on Assad to step down and for Syria to hold free elections, replacing it with a call for Assad to hand authority to his deputy and the formation of a national unity government.